Stencil printer having a construction for preventing ink leakage

Abstract: In order to prevent leaking out of ink from the perforated portion over the non-perforated stencil sheet leading end mounting portion of the stencil printing drum, in the construction that a printing drum cooperates with a back press roller or a transfer roller with a transverse bar portion of the printing drum is received in a transfer groove of the back press roller or the transfer roller, the outer circumferential length of the perforated portion of the printing drum and the transverse groove of the back press roller or the transfer roller and the relative rotation phase therebetween are so determined that the perforated portion is not laid one over the other with the transfer groove.

Description: The present invention relates to a stencil printer, and more particularly to a construction for preventing ink leakage from the printing drum of the stencil printer. A known stencil printer comprising a printing drum having a perforated construction at a circumferential portion thereof excluding two annular edge portions extending along opposite axial ends of a cylindrical configuration thereof and a strip-like stencil sheet leading end mounting portion extending between said two annular edge portions along a generatrix of said cylindrical configuration, and a back press roller having a transverse groove at an outer circumferential portion extending along a generatrix thereof, said printing drum and said back press roller being arranged to be close to and in parallel with one another so as to be rotated in mutually opposite rotational directions in synchronization with said stencil sheet leading end mounting portion aligning with said transverse groove such that a stencil sheet wrapped around said printing drum applies a stencil printing to a print sheet fed between said printing drum and said back press roller with ink supplied through said perforated portion of said printing drum is shown in Japanese Patent Application 63-28553 (JP-A-1-204781), Japanese Patent Application 1-47029 ( JP-A-2-225078), Japanese Patent Application 2-223550 ( JP-A- 4-105984) and others. It is an object of the present invention to improve the stencil printer of the above-mentioned basic construction for carrying out a stencil printing by a stencil sheet trapped around the printing drum with the ink supplied through the perforated portion of the printing drum so as to definitely prevent ink leakage from the printing drum. According to the present invention, the above-mentioned object is accomplished by the features of claim 1 and 2, respectively. The stencil printer having the above-mentioned basic construction is constructed such that the circumferential length of each of said perforated portion of said printing drum and said transverse groove of said back press roller and the relative rotation phase between said perforated portion and said transverse groove are so determined that said perforated portion is not laid one over the other with said transverse groove. Further, in the case of a stencil printer wherein a transfer roller is interposed between the printing drum and the back press - roller so that a printing image is applied onto the transfer roller by a stencil sheet wrapped around the printing drum with ink supplied through the perforated portion of the printing drum, and the ink image provided on the transfer roller is transferred onto a print sheet fed between the transfer roller and the back press roller, wherein the perforated portion of the printing drum is an outer circumferential portion thereof excluding two annular portions extending along opposite axial ends of a cylindrical configuration thereof and a strip-like stencil sheet leading end mounting portion extending between the two annular edge portions along a generatrix of the cylindrical configuration, the printing drum and the transfer roller being adapted to rotate in mutually opposite rotational direction in synchronization with one another with the stencil sheet leading end mounting portion of the printing drum aligning with the transverse groove of the transfer roller, the above-mentioned object of the present invention is accomplished by constructing the stencil printer such that the circumferential length of each of said perforated portion of the printing drum and said transverse groove of the transfer roller and the relative rotation phase between said perforated portion and said transverse groove are so determined that said perforated portion is not laid one over the other with said transverse groove. In order to obtain a stencil printing image having a uniform depth all through from the upper end to the lower end thereof, it is required that the perforated portion of the printing drum is supplied with a sufficient amount of ink to the portions thereof bordering between the perforated portion and the stencil sheet leading end mounting portion having a non-perforated construction. Therefore, when those portions are supplied with a sufficient amount of ink, such a supply of ink to those portions generally becomes excessive, generating an accumulation of an excessive ink around the leading and trailing edge portions of the perforated portion of the printing drum. In view of these, when the circumferential length of each of said perforated portion of the printing drum and said transverse groove of the back press roller or the transfer roller and the relative rotation phase between said perforated portion and said transverse groove are so determined that said perforated portion is not laid one over the other with said transverse groove, the non-perforated portion bordering said perforated portion of the printing drum is definitely applied with a pressing by the back press roller or the transfer roller once every time when the printing drum makes one rotation, so that the ink tending to flow over the outer surface of the non-perforated portion bordering said perforated portion is definitely squeezed back, thereby definitely avoiding an accumulation of ink to generate at these portions. In the accompanying drawing, Fig. 1 is a diagrammatical view of an embodiment of a stencil printer having the construction for preventing ink leakage according to the present invention, showing only those portions thereof concerned with the essence of the present invention; Fig. 2 is a diagrammatical view of an embodiment of a multiple stencil printer in which the present invention is incorporated; Fig. 3 is a diagrammatical view showing still another embodiment of a multiple stencil printer in which the present invention is incorporated; Fig. 4 is a diagrammatical view showing an embodiment of an ink pad type stencil printer in which the present invention is incorporated; Fig. 5 is a diagrammatical view showing still another embodiment of the present invention; Fig. 6 is a diagrammatical view showing the stencil printer shown in Fig. 4 in an operating condition thereof; and Fig. 7 is a diagrammatical view showing an embodiment of a stencil printer having a transfer roller in which the present invention is incorporated. In the following the present invention will be described with respect to preferred embodiments with reference to the accompanying drawing. Referring to Fig. 1 diagrammatically showing an embodiment of the stencil printer having the construction for preventing ink leakage according to the present invention about only those portions of the printing drum and the back press roller concerned with the essence of the present invention, 10 is a printing drum and 14 is a back press roller. The printing drum 10 has opposite axial ends constructed by a pair of annular portions 16 which are connected with one another by a transverse bar portion 18 extending in parallel with a central axis of the printing drum, thereby constructing the frame body of the printing drum. A flexible perforated sheet 20 having a rectangular configuration in development is mounted to seat around the outer peripheral surfaces of the pair of annular portion 16 along opposite side edge portions thereof, with a leading end portion 20a and a trailing end portion 20b of the flexible perforated sheet being respectively mounted to the transverse bar portion 18. Although in the construction shown in Fig. 1 the leading end portion 20a and the trailing end portion 20b are simply laid over the corresponding portions of the transverse bar portion 18 according to a diagrammatical illustration, a particular construction for the mounting of the trailing end portion 20b to the transverse bar portion 18 is shown in the afore-mentioned JP-A-2-225078 as well as in the Japanese Patent Application 5-306028 (JP-A-7-137415) and Japanese Patent Application 5-306029 (JP-A- 7-137416). A stencil sheet 19 is wrapped around the cylindrical surface of the printing drum 10 constructed by the flexible perforated sheet 20 with a leading end portion thereof being mounted to the transverse bar portion 18 by a clamp 21. Since the mounting construction of the leading end portion and the trailing end portion of the flexible perforated sheet to the transverse bar portion is not directly concerned with the essence of the present invention, detailed illustration and description with regard to the mounting construction are omitted. The leading end portion 20a and the trailing end portion 20b of the flexible perforated sheet 20 are both of a non-perforated construction, while an intermediate portion 20c therebetween has a perforated construction which allows ink to pass therethrough. The leading end portion 20a and the trailing end portion 20b having a non-perforated construction and the transverse bar portion 18 construct in unison a stencil sheet leading end mounting portion 10a of a strip-like non-perforated construction extending between the opposite axial ends of the printing drum along a generatrix of the printing drum 10. On the other hand, the back press roller 14 is formed with a transverse groove 22 in parallel with the central axis thereof along a generatrix thereof. The printing drum 10 and the back press roller 14 are of a same diameter as one another and are adapted to rotate in mutually opposite directions in synchronization with one another so that the stencil sheet leading end mounting portion 10a of the printing drum aligns with the transverse groove 22 of the back press roller when they oppose one another. The printing drum 10 rotates in the anticlockwise direction, while the back press roller 14 rotates in the clockwise direction, both viewed in Fig. 1 An inking roller 12 is provided inside the printing drum 10 to be rotatable with a shaft 13 thereof along a central axis thereof, with outer circumferential surface thereof being kept in contact with an inner circumferential surface of the printing drum 10. 24 is a cam adapted to cooperate with a cam follower 23 mounted on the shaft 13 of the inking roller 12 so as to bias the inking roller 12 radially inwardly of the printing drum when the transverse bar portion 18 traverses below the inking roller 12 during rotation of the printing drum, thereby it is avoided that the inking roller 12 contacts the transverse bar portion 18. 25 is a clamp for temporarily fastening a leading end of a print sheet onto the back press roller 14. As will be apparent from Fig. 1, the outer circumferential length of each of the perforated portion 20c of the printing drum 10 and the transverse groove 22 of the back press roller 14, P and G (provided that the outer circumferential length is defined to be a length along a cylindrical configuration of the printing drum or the back press roller as a whole), and the relative rotation phase between the perforated portion 20c and the transverse groove 22 are so determined that the perforated portion 20c is not laid one over the other with the transverse groove 22, so that an outer circumferential portion 30 is left between a point (actually a line) 28 on the outer circumferential surface of the back press roller corresponding to the bordering point (actually a line) 26 between the perforated portion 20c and the non-perforated leading end portion 20a of the flexible perforated sheet 20 and the transverse groove 22, while an outer circumferential portion 36 is left between a point (actually a line) 34 on the outer circumferential surface of the back press roller corresponding to the bordering point (actually a line) 32 between the perforated portion 20c and the trailing end portion 20b of the flexible perforated sheet 20 and the transverse groove 22. By the existence of these outer circumferential portions 30 and 36 on the back press roller 14, when the bordering point 26 or 32 passes through a position where it contacts with the inking roller 12 such that the squeezing action applied thereto by the inking roller 12 would urge ink through the perforated portion onto the non-perforated outer circumferential portion of the stencil sheet leading end mounting portion thereof, the ink is squeezed back by the rigid cylindrical outer circumferential surface of the back press roller 14, thereby definitely preventing the ink from leaking out beyond the bordering point 26 or 32 onto the non-perforated leading end portion 20a or trailing end portion 20b. In the Japanese Patent Application 5-306033 (JP-A-7-137419) having the same assignee and priority date as that of the present application it is described to shift the relative rotational position between the printing drum 10 and the back press roller 14 in circumferential directions from a standard position such as shown in Fig. 1 where the transverse bar portion 18 and the transverse groove 22 are just aligned with one another, for the purpose of adjusting the longitudinal position of the print image relative to the print sheet. Such a print image longitudinal position adjustment mechanism is incorporated in the printed and, the point 28 on the back press roller 14 corresponding to the bordering point 26 between the leading end portion 20a and the perforated portion of the flexible perforated sheet 20 and the point 34 on the back press roller 14 corresponding to the bordering point 32 between the trailing end portion 20b and the perforated portion of the flexible perforated sheet 20 move in biasing ranges 38 and 40, respectively. Therefore, since the magnitude of the outer circumferential portions 30 and 36 is determined by taking the biasing ranges 38 and 40 corresponding to the change of the relative rotation phase between the printing drum 10 and the back press roller 14 according to the incorporation of such a print image longitudinal position adjustment means into consideration as in the shown embodiment, the rigid squeezing back by the back press roller 14 is applied to the bordering point 26 or 32 when it passes through a position contacting the inking roller 12, regardless of the changes of the relative rotation phase between the printing drum and the back press roller 14 effected by the print image longitudinal position adjustment, thereby always definitely preventing ink from leaking out beyond the bordering point 26 or 32 onto the non-perforated leading end portion 20a or trailing end portion 20b. Fig. 2 is a diagrammatical view showing an embodiment that the present invention is incorporated into a printer for a multiplied printing proposed by Japanese Patent Application 2-223550 (JP-A-4-105984) by the same assignee as that of the present application, wherein three printing drums each having the same construction as that shown in Fig. 1 is combined with one back press roller having the same construction as that shown in Fig. 1, so as to carry out a three layered stencil printing almost at the same time. When the circumferential lengths P and G of the perforated portion and the transverse groove of each of these printing drums and the common back press roller and the relative rotation phase therebetween are determined in the same manner as described with reference to Fig. 1, it is effectively prevented that ink leaks out beyond the border between the perforated portion and the non-perforated portion over the non-perforated portion in each printing drum. In Fig. 2, the portions corresponding to those shown in Fig. 1 are designated by the same reference numerals as in Fig. 1, and since the corresponding portions make substantially the same functions, a duplicative description with respect to the embodiment shown in Fig. 2 will be omitted. Although the multiple stencil printer shown in Fig. 2 is constructed such that three printing drums cooperate with a common back press roller having the same diameter as the printing drums, a similar type of multiple stencil printer may be constructed such that three printing drums cooperate with a common back press roller having an integer times diameter of the printing drum such as two times, three times and so on. In such an embodiment, when the above-mentioned condition is satisfied with respect to the outer circumferential length of the perforated portion of each of the drums and outer circumferential length of the transverse groove of the back press roller, the leaking out of the ink from the perforated portion and the non-perforated portion in each drum is effectively prevented. Fig. 3 is a diagrammatical view similar to Fig. 2, showing an embodiment in which the back press roller has a diameter which is two times of the diameter of each printing drum. In the embodiment shown in Fig. 3, the back press roller has two transverse grooves at diametrically opposite portions and two clamps so that two sheets of printing are available by each one rotation of the back press roller. In this embodiment the outer circumferential length between the two transverse grooves of the back press roller 14 is longer than that of the perforated portion of each printing drum 10. Fig. 4 is a diagrammatical view showing an embodiment that the present invention is incorporated in a stencil printer having such a construction that the perforated portion of the printing drum is constructed by an ink pad impregnated with ink such that the ink is oozed out from the perforated portion when the perforated portion is pressed by the back press roller via a print sheet and a stencil sheet from the outer circumferential surface thereof when the printing is carried out. In this type of stencil printer, it is also effectively prevented that ink leaks out from the perforated portion over the non-perforated portion beyond the border between the perforated portion and the non-perforated portion of the printing drum when the outer circumferential lengths P and G of the perforated portion of the printing drum 10 and the transverse groove of the back press roller 4 and the relative rotation phase therebetween are so determined as described with reference to Fig. 1. In Fig. 4, the portions corresponding to those shown in Fig. 1 are designated by the same reference numerals, and since the corresponding portions make substantially the corresponding functions, a duplicative description with respect to the embodiment shown in Fig. 4 may be omitted. Fig. 5 is a diagrammatical view showing an embodiment that the present invention is incorporated into a stencil printer in which the printing drum is directly - supplied with ink such that the ink forms a deposit layer 42 when the printing drum is at rest. In Fig. 4, the portions corresponding to those shown in Fig. 1 are designated by the same reference numerals, and the corresponding portions make substantially the corresponding functions. Fig. 6 is a diagrammatical view similar to Fig. 5 showing the stencil printer shown in Fig. 5 in an operative condition that the printing drum 10 and the back press roller 14 are rotating in mutually opposite rotational directions in synchronization. As is shown in Fig. 6, the ink supplied to the inside of the printing drum is uniformly distributed over the entire inside circumferential surface of the printing drum under the action of a centrifugal force during the rotation of the printing drum so that the ink is urged out to the outside circumferential surface of the printing drum through the perforated portion 20c thereof under the pressure due to the centrifugal force acting to such an annular layer of ink. In the stencil printer in which the ink is supplied through the perforated portion of the printing drum under the action of a centrifugal force, it is also effectively prevented that the ink leaks out from the perforated portion over the non-perforated portion beyond the border therebetween of the printing drum by the outer circumferential lengths P and G with respect to the perforated portion of the printing drum and the transverse groove of the back press roller and the relative rotation phase therebetween are so determined as described with reference to Fig. 1. Fig. 7 is a similar diagrammatical view showing an embodiment that the present invention is incorporated into a stencil printer having such a construction that the stencil ink image by the printing drum 10 is formed on a transfer roller 44, and the ink image on a transfer roller is transferred onto a print sheet S fed between the transfer roller and the back press roller 14. In such a construction that the mating roller which opposes the printing drum to rotate in mutually opposite rotational direction in synchronization with the printing drum is a transfer roller which is formed with a transverse groove adapted to align with the stencil sheet leading end mounting portion of the printing drum, it is also effectively prevented that ink leaks out from the perforated portion over the non-perforated portion beyond the border therebetween in the printing drum by the outer circumferential lengths P and G with respect to the perforated portion of the printing drum and the transverse groove of the transfer roller 44 being so determined as described with reference to Fig. 1, so that the stencil printer can operate for a long period with no trouble of ink leakage. In Fig. 7, the portions corresponding to those shown in Fig. 1 are designated by the same reference numerals, and since the corresponding portions make substantially the same functions, a duplicative description will be omitted. In this connection, however, the back press roller 14 in the printing drum-transfer roller-back press roller construction shown in Fig. 7 need not necessarily be of the same diameter as the transfer roller or the printing drum, but may have a diameter substantially smaller than the transfer roller or the printing drum. In the embodiments shown in Figs. 1, 2, 3 and 7 in which the perforated portion of the cylindrical circumferential wall of the printing drum is bulged out radially outwardly as much as a small amount by the inking roller, the printing drum and the back press roller are arranged to rotate about each fixed central axis such that a clearance of several millimeters is left between the outer circumferential surface of the perforated portion of the cylindrical circumferential wall of the printing drum and the outer circumferential surface of the back press roller or the transfer roller when the perforated portion of the printing drum is not urged radially outwardly by the inking roller, and only when the printing is carried out, the stencil sheet wrapped around the printing drum is pressed against a print sheet supported by the back press roller from the rear side thereof or the outer circumferential surface of the transfer roller at the portion thereof bulged out with the perforated portion of the printing drum by the inking roller. However, the present invention is also applicable to a stencil printer in which the printing drum and the back press roller are pressed against one another by a parallel shifting of one or both of the shafts supporting the printing drum and the back press roller. Although the printing drum is a cylindrical body in the embodiments described above, the printing drum may be of the two drum type construction which itself is known as having two rolls arranged in parallel and an endless belt expanded therearound, the endless belt having a perforated construction except a stencil sheet mounting portion. In order to prevent leaking out of ink from the perforated portion over the non-perforated stencil sheet leading end mounting portion of the stencil printing drum, in the construction that a printing drum cooperates with a back press roller or a transfer roller with a transverse bar portion of the printing drum is received in a transfer groove of the back press roller or the transfer roller, the outer circumferential length of the perforated portion of the printing drum and the transverse groove of the back press roller or the transfer roller and the relative rotation phase therebetween are so determined that the perforated portion is not laid one over the other with the transfer groove.

Claims: A stencil printer comprising: a printing drum (10) having a perforated construction at a circumferential portion thereof excluding two annular edge portions (16) extending along opposite axial ends of a cylindrical configuration thereof and a strip-like stencil sheet leading end mounting portion (10a) extending between said two annular edge portions along a generatrix of said cylindrical configuration, and a back press roller (14) having a diameter which is either the same as that of said printing drum or two or higher integer times of that of said printing drum and having correspondingly either a single transverse groove (22) or said integer number of transverse grooves (22) at an outer circumferential portion or portions extending along a generatrix or generatrices thereof, said printing drum (10) and said back press roller (14) being arranged to be close to and in parallel with one another so as to be rotated in mutually opposite rotational directions in synchronization, with said stencil sheet leading end mounting portion (10a) aligning with said transverse groove (22) or grooves (22) such that a stencil sheet (19) wrapped around said printing drum applies a stencil printing to a print sheet (S) fed between said printing drum (10) and said back press roller (14) with ink supplied through said perforated portion (20c) of said printing drum, said printing drum (10) and said back press roller (14) being further relatively shiftable with respect to relative rotational position therebetween from a standard relative position where said stencil sheet leading end mounting portion (10a) of said printing drum and said single transverse groove (22) or each of said plurality of transverse grooves (22) of said back press roller are substantially aligned with one another to a first relative position in a first relative rotational direction for a first relative angle which expands a first arcuate biasing range along the circumference of said back press roller and to a second relative position in a second relative rotational direction opposite to said first relative rotational direction for a second relative angle which expands a second arcuate biasing range along the circumference of said back press roller, wherein the sum of the circumferential length (P) of said perforated portion (20c) of said printing drum and said first and second arcuate biasing ranges (38, 40) is smaller than the circumferential length of a part of said back press roller (14) having said single transverse groove (22) excluding said transverse groove (22) or the circumferential length of a part of said back press roller having the plurality of transverse grooves (22) extending between each two adjacent transverse grooves (22). A stencil printer comprising: a printing drum (10) having a perforated construction at a circumferential portion thereof excluding two annular edge portions (16) extending along opposite axial ends of a cylindrical configuration thereof and a strip-like stencil sheet leading end mounting portion (10a) extending between said two annular edge portions along a generatrix of said cylindrical configuration, a transfer roller (44) having a diameter which is the same as that of said printing drum and having a transverse groove (22) at a circumferential portion thereof along a generatrix thereof, and a back press roller (14), said printing drum (10) and said transfer roller (44) being arranged to be close to and in parallel with one another with said stencil sheet leading end mounting portion (10a) aligning with said transverse groove (22) so as to be rotated in mutually opposite rotational directions in synchronization, while said transfer roller (44) and said back press roller (14) are arranged to be close to and in parallel with one another so as to be rotated in mutually opposite rotational directions in synchronization, such that a stencil sheet (19) wrapped around said printing drum (10) applies an ink image onto said transfer roller (44) by ink supplied through said perforated portion (20c) of said printing drum (10), while said ink image on said transfer roller (44) is transferred onto a print sheet (S) fed between said transfer roller (44) and said back press roller (14), said printing drum (10) and said transfer roller (44) being further relatively shiftable with respect to relative rotational position therebetween from a standard relative position where said stencil sheet leading end mounting portion (10a) of said printing drum and said transverse groove (22) of said transfer roller are substantially aligned with one another to a first relative position in a first relative rotational direction for a first relative angle which expands a first arcuate biasing range along the circumference of said transfer roller and to a second relative position in a second relative rotational direction opposite to said first relative rotational direction for a second relative angle which expands a second arcuate biasing range along the circumference of said transfer roller, wherein the sum of the circumferential length (P) of said perforated portion (20c) of said printing drum and said first and second arcuate biasing ranges is smaller than the circumferential length of a part of said transfer roller (44) excluding said transverse groove (22). A stencil printer according to claim 1 or 2, wherein supply of ink through said perforated portion (20c) of said printing drum (10) is substantially energized by a squeezing action by an inking roller (12) contacting an inside surface of said printing drum (10). A stencil printer according to claim 1 or 2, wherein the supply of ink through said perforated portion (20c) of said printing drum (10) is substantially energized by oozing out of ink from said perforated portion (20c) due to a compression applied thereto. A stencil printer according to claim 1 or 2, wherein the supply of ink through said perforated portion (20c) of said printing drum (10) is substantially energized by a centrifugal force acting to the ink due rotation of said printing drum (10).

Inventors: TAKAHASHI YASUHIRO, TAKITA NAGON, TAKAHASHI, YASUHIRO, TAKITA, NAGON, TAKAHASHI, YASUHIRO, C/O RISO KAGAKU CORP., TAKITA, NAGON, C/O RISO KAGAKU CORP.
Applicants: RISO KAGAKU CORP, RISO KAGAKU CORPORATION
Application year: 1994
Main classification: B41L13
IPC codes: B41L13